Wireless communication systems enable users of User Equipment (UE) to communicate with other such users via one of a number of base stations and via one or a number of core networks. Typically, the UEs are mobile terminals, such as mobile (cellular) telephones and the like, although the term UE may also refer to generally stationary communication devices, such as laptop computers, web browsers, machine-type communication devices, and the like. In the following description the term mobile communication device is used, which is intended to cover any type of such user equipment (mobile and stationary).
In an active or connected state a mobile communication device is registered with the network and has a Radio Resource Control (RRC) connection with a base station so that the network knows to which base station (or cell thereof) the mobile communication device belongs and can transmit data to and receive data from the mobile communication device. Each mobile communication device also establishes a default Evolved Packet System (EPS) Bearer (i.e. an end-to-end dedicated communication path) from the mobile communication device to an endpoint beyond the base station, typically a gateway (such as a packet data network gateway—‘PDN-GW’ or ‘P-GW’—or the like), in the Enhanced Packet Core (EPC) network, or core network for short. An EPS Bearer, which is specific to the mobile communication device, defines a transmission path through the network and assigns an IP address to the mobile communication device, at which it can be reached by other communication devices, such as another mobile communication device. When data is sent to the mobile communication device via such an EPS bearer or via another dedicated bearer, this is referred to as a unicast transmission.
However, in order to reduce the amount of data that needs to be sent over the air interface (which has limited resources) when a plurality of mobile communication devices are receiving the same data (e.g. popular content, such mobile TV programs and the like), broadcast and/or multicast services may also be used instead of separate unicast transmission for each mobile communication device. In this case, e.g. when a group of mobile communication devices are interested in the same content, rather than using each mobile communication device's dedicated bearer, the network sends the data in a synchronised manner to the whole group in a single broadcast or multicast transmission, using a common broadcast/multicast bearer provided between the network and the mobile communication devices of that group.
As part of the Long Term Evolution (LTE) of UTRAN (UMTS Terrestrial Radio Access Network) referred to as E-UTRAN, proximity-based services (ProSe) have been introduced, which make use of direct device-to-device (D2D) communication bearers directly between compatible mobile communication devices rather than indirect bearers provided from one mobile communication device, via a base station and the core network, to another mobile communication device (e.g. a pair of EPS bearers and/or broadcast/multicast bearers). Thus, when a ProSe enabled mobile communication device is within the transmission range of (or served by the same base station as) another ProSe mobile communication device, they can communicate user data without the need to use core network resources. Such services can be achieved by establishing a special, ‘D2D’, bearer between the mobile communication devices in direct communication (or communication routed via their base station only) instead of their default or other conventional EPS bearers (which might be still used for other types of communications). This direct or locally routed communication could result in better utilization of the available resources, especially on the radio interface, where these are limited. Details of the ProSe functionality have been specified in the 3GPP Technical Report TR 22.803 document, the contents of which are incorporated herein by reference.
More recently the provision of a relay functionality, in the mobile communication device, using the ProSe functionality has been proposed to allow one mobile communication device (referred to as a ‘UE-Relay’ or ‘UE-R’) to relay the signalling and the user data for another mobile communication device to and from the network, even if the other mobile communication device is not located within the network's coverage. In this case, the relayed mobile communication device can communicate with the network (both user plane and control plane data) via the UE-R thus accessing the same services as if the relayed mobile communication device were served by a base station of the network.
Public safety communities (e.g. emergency services) that are committed to using LTE are also interested in such proximity-based services, especially in situations when network coverage is limited (see e.g. 3GPP SP-120456 (MoU between TETRA & Critical Communications Association (TCCA) & the National Public Safety Telecommunications Council), and 3GPP S1-121247 (TCCA)). Thus ProSe allows LTE network operators to achieve economy of scale, i.e. that the same network and/or the same technology can be used for both public safety and non-public-safety services.
In order to be able to benefit from ProSe services, a ProSe enabled mobile communication device performs a so-called discovery procedure (which can be done with or without network assistance/coverage). As part of this discovery procedure, each ProSe enabled mobile communication device transmits (e.g. periodically) a beacon for announcing itself to other such mobile communication devices in its proximity, and also listens for beacon transmissions by other devices. After two (or more) mobile communication devices have mutually discovered each other (e.g. they have received the other mobile communication device's beacon), they are able to start a ProSe communication session with each other.
The so-called Multimedia Broadcast/Multicast Service (MBMS) and the enhanced MBMS (eMBMS) technologies may be used for the simultaneous broadcast and/or multicast of content to groups of mobile communication devices. In a typical (e)MBMS use case, users subscribe to a service (e.g. mobile TV or the like) that they wish to receive on their mobile communication devices. Each mobile communication device is assigned to a group (or groups) in dependence on the user's subscription(s), and receives associated broadcast and/or multicast content from the network in the form of a synchronised transmission via its serving base station or via multiple base stations at the same time (e.g. inside the same Multicast-Broadcast Single-Frequency Network (MBSFN) Area). The main benefit of (e)MBMS is that instead of transmitting the content to each mobile communication device via its individual associated EPS bearer (which might add up to hundreds or thousands of EPS bearers in the case of popular content), in (e)MBMS data is transmitted only once and at the same time to all mobile communication devices within any one group, via the base station(s) serving mobile communication devices belonging to that group. This approach beneficially reduces the congestion in the core network and/or the resources required by the UEs in the radio access network (RAN).